Methods and apparatus for retractable pin friction stir welding and spot welding

ABSTRACT

An apparatus for friction stir welding is described that includes a stationary assembly having a bore therethrough, the bore having an inner diameter, and a rotational assembly having a welding end. At least the welding end of the rotational assembly extends through the bore. A portion of the rotational assembly is adjacent the inner diameter of the bore. At least one of the adjacent portion of the rotational assembly and the inner diameter of the stationary assembly are configured such that rotation of the rotational assembly will cause plasticized material from a welding process that has entered an area between the adjacent portion and the inner diameter to move towards a welding zone located proximate the welding end.

BACKGROUND

This disclosure relates generally to welding processes and morespecifically, to methods and systems to facilitate flash reduction andweld integrity in friction stir welding processes.

Friction stir welding is typically utilized for joining together workpieces of materials such as metals and plastics. A friction stir weldingtool has a shoulder at its distal end and a non-consumable rotatablewelding pin extending downward centrally from the shoulder. Some knownfriction stir welding tools include a shoulder fixed in position withrespect to the pin and other known friction stir welding tools include apin that is movable with respect to the shoulder.

In a typical friction stir weld operation, two work pieces are supportedon a backing plate and are positioned so that the work piece edges wherethe weld is to be formed are held in direct contact to form aninterface. The tool is then positioned so that the rotating pin is incontact with the work pieces at the interface. The rotation of the pinagainst the work piece materials produces a large amount of frictionalheating in both the welding pin and the plate. This heat causes the workpiece materials to soften in the vicinity of the rotating pin, whichresults in the formation of a weld.

In one form of friction stir welding, the tool is moved longitudinallyalong the interface between the two work pieces, thereby forming anelongate weld along the interface. The welding tool shoulder facilitatesreducing softened, or plasticized, work piece materials from escapingupwards and away from the weld being formed. When the weld operation iscompleted, the welding tool is retracted.

Known drive apparatus are utilized to move, or drive, the welding toolalong the weld path. One known drive apparatus includes a conventionalmilling machine used in metalworking. Such milling machines areparticularly suited to maintain a fixed gap between the distal end ofthe pin tool and the surface of the backing plate. Another type of knowndrive apparatus is known as a “constant vertical force machine”, and itapplies a downward force along the vertical axis of the pin until apredetermined force is reached. This type of “constant vertical force”machine is particularly suited to maintaining a precise contact betweenthe friction stir welding tool shoulder and the upper surface of thematerials to be welded.

The above described friction stir welding processes are sometimesreferred to as continuous path retractable pin tool welding. During suchwelding process, parent materials are heated to a plastic or malleablestate. As explained above, as the parent materials soften, such softenedmaterials tend to migrate or draw up between an outer diameter of thetool and an inner diameter of the shoulder holding the pin. As a result,some amount of the plasticized materials between the two surfacesescapes from the weld process, and such lost material is commonlyreferred to as flash. The volume of material that migrates away from theweld can sometimes cause anomalies such as voids and undesirable surfaceindentations.

Another known friction stir welding process is commonly referred to asfriction stir spot welding. During friction stir spot welding, parentmaterials are heated to a plastic or malleable state. As these materialssoften, they also tend to migrate up between the outer diameter of thetool shoulder and the inner diameter of a clamping anvil, allowing theplasticized parent materials between the two surfaces to escape from theweld process. As with the continuous path retractable pin tool weldingprocess, the volume of material that migrates away from the weld cansometimes cause anomalies such as voids and undesirable surfaceindentations.

BRIEF DESCRIPTION

In one aspect, apparatus for friction stir welding is provided. Theapparatus includes a stationary assembly comprising a bore therethrough,the bore comprising an inner diameter, and a rotational assemblycomprising a welding end. At least the welding end of the rotationalassembly extends through the bore. A portion of the rotational assemblyis adjacent said inner diameter of said bore. At least one of theadjacent portion of the rotational assembly and the inner diameter ofthe stationary assembly is configured such that rotation of therotational assembly will cause plasticized material from a weldingprocess that has entered an area between the adjacent portion and theinner diameter to move towards a welding zone located proximate thewelding end.

In another aspect, a method for reintroducing an amount of flashmaterial migrating into an area between adjacent portions of arotational assembly and a stationary assembly that substantiallysurrounds the rotational assembly back into a friction stir weldingprocess is provided. The method comprises rotating the rotationalassembly to form a weld, engaging flash material migrating into an areabetween the adjacent portions of the rotational assembly and thestationary assembly with a spiraling mechanism formed on at least one ofan outer diameter of the rotational assembly and an inside diameter ofthe stationary assembly, and utilizing the spiraling mechanism incombination with the rotation of the rotational assembly to push theflash material back into a welding zone proximate the rotationalassembly.

In still another aspect, a friction stir welding apparatus is provided.The welding apparatus includes a rotational assembly having an outerdiameter, and a stationary assembly having an inner diametersubstantially adjacent to the rotational assembly. At least one of therotational assembly inner diameter and the stationary assembly outerdiameter have material control threads in a direction opposite adirection of rotation of the rotational assembly.

In yet another embodiment, a method for material management in frictionstir welding processes is provided. The method comprises providing afriction stir welding apparatus comprising a rotating tool within asleeve, configuring the rotating tool to rotate in a first direction,and outfitting at least one of the rotating tool and the sleeve with atleast one of a material control groove and a material control protrusionspiraling in a direction counter to the direction of rotation of therotating tool.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a friction stir spot welding device.

FIG. 2 is a detailed cross-sectional view of a clamping anvil, shouldertool, and pin tool for the friction stir spot welding device of FIG. 1,illustrating migration of plasticized material.

FIG. 3 is a detailed cross-sectional view of a clamping anvil configuredwith helical grooves therein.

FIG. 4 is a detailed cross-sectional view illustrating an effect of thehelical grooves on the migration of plasticized material.

FIG. 5 is a cross-sectional view of a retractable pin tool friction stirwelding device.

FIG. 6 is a detailed cross-sectional view of a shoulder tool and pintool for the friction stir welding device of FIG. 5, illustratingmigration of plasticized material.

FIG. 7 is a detailed cross-sectional view of the shoulder toolconfigured with helical grooves therein.

FIG. 8 is a detailed cross-sectional view illustrating an effect of thehelical grooves on the migration of plasticized material.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional view of a friction stir spot welding device10. Spot welding device 10 includes a spindle housing 12 attached to aclamping housing 14. As illustrated in FIG. 1, spindle housing 12 andclamping housing 14 define a cavity 16. Cavity 16 extends through abottom 18 of clamping housing 14 and defines a bore 20. A shoulder tool22 is configured to be inserted into bore 20. Shoulder tool 22 is heldin place by a shoulder spindle 30 and locking screws 32. Shoulderspindle 30 has a bore therethrough in which is held a pin spindle 40 anda pin tool 42. Pin tool 42 and shoulder tool 22 extend through bore 20of clamping housing 14 and are retained in place by a clamping anvil 50.

FIG. 2 is a detailed cross-sectional view of clamping anvil 50, shouldertool 22, and pin tool 42 of friction stir spot welding device 10, andillustrates migration of plasticized material. In one embodiment,shoulder tool 22 and pin tool 42 rotate counterclockwise when engaging amaterial to be spot welded. This process softens or plasticizes thematerial to be welded and a portion of this material M tends to migratethrough a narrow passageway 60 between clamping anvil 50 and shouldertool 22. A portion of this material M may migrate all the way to cavity16. Migration of this material away from the welding zone results of aloss of material M at the welding zone (adjacent a welding end 62 of pintool 42) which may lead to surface anomalies and other indentations inthe parts that are being welded.

FIG. 3 is a detailed cross-sectional view of a clamping anvil 100configured with helical grooves 102 therein. Helical grooves 102 definea threaded area located on an inner diameter 104 of clamping anvil 100,concentric to the outer diameter of the shoulder tool (not shown in FIG.3). Helical grooves 102 provide a mechanism through which materialmigrating up through passageway 60 (shown in FIG. 2) is forced back downinto a welding zone adjacent pin tool 42. Helical grooves 102 aresometimes referred to as material control grooves. The counterclockwiserotation of pin tool 42 and shoulder tool 22 results in materialmigrating through the narrow passageway 60 as shown in FIG. 2. Therotation of the material in passageway 60 coupled with grooves 102results in the material being pushed, or forced, back down into thewelding zone adjacent a welding end 62 of pin tool 42. In a specificembodiment, grooves 102 are approximately 0.017 inch in depth and have apitch of 0.005 inch.

FIG. 4 is a detailed cross-sectional view of clamping anvil 100,shoulder tool 22, and a pin tool 42, and illustrates an effect ofhelical grooves 102 on the migration of plasticized material M. In FIG.4, shoulder tool 22 is illustrated as rotating and clamping anvil 100 isfixed (non-rotating). Shoulder and pin friction stir welding tools 22and 42 can be independently driven or linked together to the same drivespindle (e.g. shoulder spindle 30 shown in FIG. 1). The pin and shouldertools 22 and 42 are rotating before pin tool 42 is inserted into theinterface between the materials to be welded. As pin tool 42 proceeds toa preprogrammed position or depth, material M (i.e., flash) isvolumetrically displaced around pin tool 42. Material M migrates betweenthe shoulder tool outer diameter and the clamping anvil inner diameter.As shown in FIG. 4, rotation of shoulder tool 22 and grooves 102 formedwithin clamping anvil 100 work concurrently to push or pump material Mback into a welding zone 110, thereby reducing flash material. Withrespect to friction stir spot welding devices, pin tool 42 and shouldertool 22 are sometimes collectively referred to herein as a rotationalassembly, and clamping anvil 100 is sometimes referred to as astationary assembly.

FIG. 5 is a cross-sectional view of a retractable pin tool friction stirwelding device 200. The friction stir welding device 200 includes aspindle housing 202 having a bore 203 there through. Within bore 203 islocated a shoulder spindle 204. Extending from a bottom 205 of shoulderspindle 204 is a shoulder tool 206. An upper portion of the shouldertool 206 is fixed within a larger diameter bore 207 within shoulderspindle 204 by locking screws 208. Above the placement of shoulder tool206, a smaller diameter bore 210 extends through shoulder spindle 204from shoulder tool 206 through a top 211 of shoulder spindle 204. Withinbore 210 is located a pin spindle 212 from which extends an upperportion of a pin tool 214. Pin tool 214 extends through a portion ofshoulder spindle 204 and all the way through the shoulder tool 206. Pintool 214 rotates and a bottom section 220 of pin tool 214 engages thematerials to be welded as further discussed below.

FIG. 6 is a detailed cross-sectional view of a bottom portion 220 of pintool 214 and a bottom portion 222 of shoulder tool 206 of the frictionstir welding device 200 of FIG. 5. FIG. 6 further illustrates, migrationof plasticized material M. Retractable pin tool friction stir weldingdevice 200 is utilized in a continuous welding path and pin tool 214 isconfigured in one embodiment to rotate with respect to shoulder tool206. During this welding process the material to be welded is engaged bypin tool 214 and is plasticized due to the rotation of pin tool 214. Therotation of pin tool 214 also causes a portion of the plasticizedmaterial to tend to migrate to an area 230 between an outer diameter ofpin tool 214 and an inner diameter of shoulder tool 206.

FIG. 7 is a detailed cross-sectional view of a shoulder tool 250configured with helical grooves 252 formed within an inner diameter 254of shoulder tool 250. Helical grooves 252 provide a mechanism throughwhich material migrating up through passageway 230 is forced back downinto a welding zone adjacent pin tool 214. Helical grooves 252 aresometimes referred to as material control grooves. The rotation of pintool 214 and shoulder tool 206 both (shown in FIG. 6) results inmaterial M rotating within the narrow passageway 230 as shown in FIG. 6.The rotation of the material M in passageway 230 coupled with grooves252 and the rotation of the material results in the material beingpushed, or forced, back down into the welding zone adjacent bottomportion 220 of pin tool 214. In a specific embodiment, grooves 252 areapproximately 0.017 inch in depth and have a pitch of 0.005 inch.

FIG. 8 is a detailed cross-sectional view of shoulder tool 252 and a pintool 214 and illustrates an effect of helical grooves 252 formed withinshoulder tool 250 on the migration of plasticized material M in acontinuous path retractable pin tool welding process. Helical grooves252 define a threaded area located on the inner diameter of shouldertool 250 adjacent to a pin tool 214. The pin tool 214 and shoulder tool250 are independently driven and are rotating before pin tool 214 isinserted into the interface between the materials to be welded. As thepin 214 tool proceeds to a preprogrammed position or load controlleddepth, plasticized material M (i.e., flash) is volumetrically displacedaround the pin tool 214. As shoulder tool 250 engages the surface to bewelded, and pin tool 214 traverses along a preprogrammed materialinterface path, softened flash material M migrates up pin tool 214between the outer diameter of pin tool 214 and the adjacent innerdiameter 254 of shoulder tool 250. As shown in FIG. 8, independent pintool 214 and shoulder tool 250 rotation and helical grooves 252 formedin shoulder tool 250 work concurrently and to push or guide flashmaterial M back into a welding zone 270 reducing an amount of flashmaterial. With respect to retractable pin tool friction stir weldingdevices, pin tool 214 is referred to as a rotational assembly andshoulder tool 250 is referred to as a stationary assembly.

While described herein with respect to grooves formed in a stationaryassembly, is to be understood that other configurations may be utilizedto push flash material back into a welding zone. Specifically, ratherthan the stationary assembly, the rotational assembly may be formed withthe above described material control grooves. In other embodiments,material control protrusions with dimensions similar to the abovedescribed grooves may be formed on the rotational assembly or thestationary assembly. In any of the embodiments, flash material engagingthe grooves or protrusions coupled with the rotation of the rotationalassembly causes the plasticized flash material to be guided back into awelding zone.

While described herein with respect to a spot welding apparatus and aretractable pin welding apparatus, it is to be understood that theforegoing description can be applied to other friction stir weldingapplications including any friction stir welding process where eitherthe pin tool is fixed with respect to a shoulder tool or friction stirwelding processes where the pin tool and shoulder tool move with respectto one another to provide tapered welds. The reduction of lost materialin the various embodiments thereby result in enhanced weld quality,surface finish and weld integrity. The finished products in any of theseembodiments is a welded material or article of manufacture that has beenjoined in a friction stir welding process where the welded material hasa larger volume of welded material due to less flash material being lostdue to the welding process as above described.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A friction stir welding apparatus comprising: a non-rotationalassembly comprising a bore therethrough, said bore defining an innerdiameter; and a rotational assembly comprising a welding end, at leastsaid welding end of said rotational assembly extending through saidbore, a portion of the remainder of said rotational assembly comprisinga cylindrical surface that is adjacent said inner diameter, said innerdiameter comprising material control threading having a plurality ofthreads arranged along a line substantially parallel to the rotationalassembly; and said cylindrical surface comprising a smooth surface suchthat rotation of said rotational assembly will cause plasticizedmaterial from a welding process that has entered an area between thecylindrical surface and said inner diameter to move towards a weldingzone located proximate said welding end.
 2. A friction stir weldingapparatus according to claim 1 wherein said apparatus is a friction stirspot welding apparatus, said rotational assembly comprises a pin tooland a shoulder tool, and said non-rotational assembly comprises aclamping anvil that includes said inner diameter.
 3. A friction stirwelding apparatus according to claim 2 wherein said material controlthreading comprises a plurality of grooves formed in said inner diameterof said clamping anvil, said grooves adjacent said shoulder tool, saidgrooves, based on rotation of said shoulder tool, positioned to pushplasticized material back into the welding zone.
 4. A friction stirwelding apparatus according to claim 2 wherein said material controlthreading comprises a plurality of protrusions formed on said innerdiameter of said clamping anvil, said protrusions adjacent said shouldertool, said protrusions, based on rotation of said shoulder tool,positioned to push plasticized material back into the welding zone.
 5. Afriction stir welding apparatus according to claim 2 wherein saidshoulder tool comprises an outer diameter adjacent said inner diameterof said clamping anvil, said material control threading comprising atleast one of a plurality of grooves formed in said outer diameter ofsaid shoulder tool and a plurality of protrusions extending from saidouter diameter of said shoulder tool, said protrusions and said grooves,based on a rotation of said shoulder tool, positioned to pushplasticized material entering into an area between said shoulder tooland said clamping anvil back into the welding zone.
 6. A friction stirwelding apparatus according to claim 1 wherein said apparatus is aretractable pin tool friction stir welding apparatus, said rotationalassembly comprises a pin tool and said non-rotational assembly comprisesa shoulder tool that includes said inner diameter.
 7. A friction stirwelding apparatus according to claim 6 wherein said material controlthreading comprises a plurality of grooves formed in said inner diameterof said shoulder tool, said grooves adjacent said pin tool, saidgrooves, based on rotation of said pin tool, positioned to pushplasticized material back into the welding zone.
 8. A friction stirwelding apparatus according to claim 6 wherein said material controlthreading comprises a plurality of protrusions formed on said innerdiameter of said shoulder tool, said protrusions adjacent said pin tool,said protrusions, based on rotation of said pin tool, positioned to pushplasticized material back into the welding zone.
 9. A friction stirwelding apparatus according to claim 6 wherein said pin tool comprisesan outer diameter adjacent said inner diameter of said shoulder tool,said material control threading comprising at least one of a pluralityof grooves formed in said outer diameter of said pin tool and aplurality of protrusions extending from said outer diameter of said pintool, said protrusions and said grooves, based on a rotation of said pintool, positioned to push plasticized material entering into an areabetween said shoulder tool and said pin tool back into the welding zone.10. A friction stir welding apparatus according to claim 1 wherein saidmaterial control threading comprises a plurality of grooves formed insaid inner diameter of said non-rotational assembly, said grooves, basedon rotation of said rotational assembly, positioned to push any flashmaterial back into the welding zone.
 11. A friction stir weldingapparatus comprising: a rotational assembly comprising an outer diameterthat defines a substantially cylindrical surface; and a non-rotationalassembly comprising a bore therethrough that defines an inner surface,the inner surface substantially adjacent to a portion of thesubstantially cylindrical surface of said rotational assembly, saidinner surface comprising material control threading having a pluralityof threads arranged along a line substantially parallel to therotational assembly in a direction opposite a direction of rotation ofsaid rotational assembly, and the adjacent portion of the substantiallycylindrical surface having a smooth surface.
 12. A friction stir weldingapparatus according to claim 11 wherein said rotational assemblycomprises a welding end, said threading and a rotation of saidrotational assembly configured to cause any plasticized material betweensaid rotational assembly and said non-rotational assembly to movetowards a welding zone located proximate said welding end.
 13. Afriction stir welding apparatus according to claim 11 wherein saidmaterial control threading comprises a plurality of grooves formed insaid inner surface of said non-rotational assembly.
 14. A friction stirwelding apparatus according to claim 13 wherein said apparatus comprisesa friction stir spot welding apparatus and said non-rotational assemblycomprises a clamping anvil.
 15. A friction stir welding apparatusaccording to claim 13 wherein said apparatus comprises a retractable pintool friction stir welding apparatus and said non-rotational assemblycomprises a shoulder tool.